It'd be much less lag to use the larger icon since you don't have to update each chunk when it moves with sync steps, however you won't get the appropriate collision detection as the larger icon would still only register as a single object and as a result, only take up one space. If you're only going to have one or two of them in the field at any time then chunks with sync steps, if these are a common appearance then maybe large icons. Though I don't think it'd really matter.